How well does the local climate zone scheme discern the thermal environment of Toulouse (France)? An analysis using numerical simulation data

Dans quelle mesure le schéma des zones climatiques locales discerne-t-il bien l'environnement thermique de Toulouse (France) ? Une analyse utilisant des données de simulation numérique

Kwok, Yu Ting ; Schoetter, Robert ; Lau, Kevin Ka-Lun ; Hidalgo, Julia ; Ren, Chao ; Pigeon, Grégoire ; Masson, Valéry

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<p align=justify>To build healthy, resilient, and climate-responsive cities, planners need ways to understand the local complexities of urban thermal climates. To assist in meeting this need, this study employs the simple classification of "local climate zones" (LCZs) to conduct a spatiotemporal thermal climatic analysis of the Toulouse Metropolitan Region (France) under warm and dry summer conditions. Simulations are performed using the mesoscale atmospheric model Méso-NH. These simulations provide a city-wide spatial coverage of 2-m air temperature (T2M), mean radiant temperature (MRT), and Universal Thermal Climate Index (UTCI). Model parameters describing the urban morphology are initialized based on administrative databases and independent of LCZ maps, which allows for an evaluation of whether the distributions of the modelled thermal climatic parameters will differ between LCZs. The results show that different LCZs possess significantly different distributions of T2M and MRT, confirming the suitability of the LCZ scheme for discerning the thermal environment of Toulouse. Compact urban settings (LCZ 1/2/3) show the highest T2M throughout the day and a nocturnal temperature difference of up to 2.8 K compared to rural settings. The MRT of LCZ 1/2/3 in the late afternoon (1700-2000 LST (UTC + 2)) can be as much as 6.3 K lower than it is for LCZs with open settings due to shading by dense urban structures. Additional analysis reveals that the intra-LCZ variabilities of T2M and MRT may be explained by the distance to the city centre. Finally, the thermal stress in different LCZs is assessed with the modelled UTCI. Among the built LCZs, the probability of strong heat stress is the highest for open high/mid-rise (LCZ 4/5) and lowest for sparsely built (LCZ 9) and open low-rise (LCZ 6) settings. For land cover type LCZs, dense trees (LCZ A) are the most favourable for daytime outdoor human thermal comfort.</p>
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